System and process for active vibration damping

ABSTRACT

An active vibration damping system for a drive unit having at least one drive shaft is provided. The vibration damping system includes a flywheel which comprises a movable base element of a linear electric motor that acts on the rotation of the shaft. The linear electric motor consists of a linear machine which generates a traveling magnetic field. The turning direction of the traveling magnetic field chosen relative to the turning direction of the crankshaft such that when unacceptably low momentary turning rates are sensed, a thrust force is applied to the flywheel and when unacceptably high momentary turning rates are sensed, a retarding force is applied until an evening up of the crankshaft rotation or a rotary vibration damping is achieved.

FIELD OF THE INVENTION

The invention relates to a system and process for active vibrationdamping of a drive unit having a rotating shaft, and more particularlyto a system that maintains turning-speed irregularities of the rotatingshaft within selected values by utilizing a flywheel or other memberseated on the shaft as a movable base element of an electrical machineand a system for its execution.

BACKGROUND OF THE INVENTION

Substantial sound or noise sources in a motor vehicle may include theinternal-combustion engine itself as well as the connected drivecomponents, such as crankshaft, drive shaft, and also the exhaustinstallation, tire noises, etc. One of the principal sources of noise ina motor vehicle are shafts driven from a drive unit or situated therein.These include the crankshaft, the Cardan shaft, the drive shaft, etc.Internal-combustion engine drive units have, in driving operation,deviations from a predetermined desired turning rate in many or allturning rate zones. Such rotation irregularities or turning-ratedisturbances, are caused, for example, by non-uniform combustion in aone-cylinder configuration or by "dropping out" of one cylinder in amulticylinder configuration. They typically cause undesired interferencevibrations of the off-drive shaft, especially of the crankshaft, whichare transferred to other components of the vehicle and often result in atroublesome noise level.

Some systems have been developed for reduction of noise levelsassociated with a vehicle during its driving operation and experiencedby the vehicle occupants. For example, known systems for noise reductionin a vehicle by active vibration damping include DE 39 39 828 C2 and EP0 372 590 B1. These documents describe systems that detect the phase andamplitude of undesired vibration from all the sound sources andsuperimpose an opposite vibration to the source. For example, when thephase of a vibration and amplitude is detected from the vehicle bodywork, the system superimposes an equal-amplitude additional countervibration. These systems require an additional corresponding vibrationsource which transfers the counter vibrations, for example, to thevehicle body-work. The systems for active vibration damping described inthe publications DE 41 41 637 A1 and G 91 04 812 U1 operate insubstantially the same fashion.

Other documents, DE 36 23 627 A1 and DE 32 30 607 A1, describe methodsfor monitoring the turning-rate behavior in the drive-line of aninternal-combustion engine to detect rotation irregularities. From thesedetected irregularities, a control arrangement generates signals forcontrolling a correcting element, possibly in the form of a slipcoupling or a three-phase current electric motor where the coupling orrotor of the electric motor is coupled with the crankshaft of theinternal-combustion engine. Further, DE-OS 30 05 561 discloses avibration damping system with an eddy current brake utilized as thecorrecting element. The vibration damping system disclosed inpublication DE 41 00 937 A1 measures possible rotation irregularities ofa crankshaft and damps these irregularities with an alternating-currentsynchronous motor.

Patent Abstracts of Japan, Volume 4, No. 29 (M-002), Mar. 14, 1980,disclose a device for active vibration damping of an internal-combustionmotor, the crankshaft of which is equipped with a flywheel. A magnetyoke grips the flywheel in a small zone of the flywheel circumference.The magnet yoke and the flywheel together provide an eddy-current brakeutilized as a correcting member.

Other known systems, as noted in the following documents, are directedto partial aspects of active vibration damping. For example, EP 70 553B1 describes an electrical machine for influencing the turning rate of agas turbine and DE 453 179 A1 describes a device for monitoring theturning rate of a turbine off-drive shaft in a current-producinggenerator.

A principal disadvantage of these known vibration-damping systems is therequirement of additional relatively complicated vibration sources forthe generation of counter vibrations. The success of noise suppressiondepends strongly on the location, the form and the material of thevehicle surfaces upon which the counter-vibrations are applied whichfurther complicates such systems. Furthermore, the aforementionedcorrecting members for influencing shaft movement of a rotating shaftrequire great expenditures of space due to their structural size.

SUMMARY OF THE INVENTION

Accordingly, it is a general object of the invention to provide a systemand process for active vibration damping which are less expensive thanknown methods and systems and are suited especially for motor vehiclesand the like.

It is an additional object of the present invention to provide an activevibration damping system that minimizes additional weight of thevehicle.

It is a further object of the present invention to provide noisesuppression in a motor vehicle or the like with the use of acompensating system that eliminates vibration disturbances due torotational irregularities in a driven shaft.

The invention meets these objectives with an active vibration dampingsystem including a correcting member provided as an electrical linearmachine or a linear motor. A method according to the invention providesactive vibration damping in drive units with at least one rotating shaftby limiting turning rate irregularities to within selected values. Themethod is performed with a flywheel seated on the shaft used as amovable element of a linear machine.

The invention prevents noise formation in drive shafts or the like bymonitoring the potential disturbance source, the momentary value of theturning rate or the angular segment speed of the shaft, and providessensing signals to a regulating or control circuit. The control circuitderives correction signals to regulate the momentary turning rate of theshaft within desired values. When possible deviations are detected, thesystem provides correction signals to automatically adjust or maintainthe turn rate. Deviations from a predetermined desired value, therefore,are immediately corrected. The desired value usually corresponds thereto the optimal noise conditions of a crankshaft in a motor vehicle,i.e., to a noiseless, or at least to a low-noise, travelling operation.

Rather than employing additional sources of vibration, the inventionattacks and suppresses the vibration or noise sources involved directly,and suppresses the vibration disturbances caused by rotationirregularities of the rotating shafts at the point of origination.Accordingly, the formation of disturbance vibrations and theaccompanying noises in the vehicle is avoided. The invention, therefore,pursues a different course than that of the earlier-described state ofthe art.

The invention provides further important advantages. The long termconsequences of vibration stress applied to the drive shaft such asmaterial fatiguing and perhaps "dropping-out" of the shaft are avoided.Further, the vibration system of the invention optionally replaces therotary vibration eradicators hitherto used in vehicle technology. Suchrotary vibration eradicators are known, for example, from EP O 250 913A2 or from DE 89 07 426.2 U1 assigned to the assignee of the presentinvention. They are formed mainly as "passive" vibration additionalmasses fabricated of rubber and located concentrically about the shaft.They suffer the disadvantage that they are generally tunable only to onevibration frequency and, in addition to additional cost, they add to theoverall vehicle weight.

In the preferred embodiment, the invention uses a linear machine toinfluence the rotation of the shaft. Such linear machines utilize theprinciple of electromagnetic induction or Lorentz force. Theyconventionally include a stationary base element (stator) and a movingbase element (rotor) that are separated spatially and bodily by an airgap. The stator and rotor are linked with one another over a magneticflux passing in common through the gap. At least one of the baseelements generates the magnetic primary field with the aid of one ormore exciter windings as a traveling magnetic field. The other baseelement includes one or more electric conductors. The primary field ofthe first base element traverses the gap separating the base elementsand through flux linkage, induces a driving Lorentz force. The exciterwindings may be arranged on the stationary (stator) or on the movablebase element (rotor). Accordingly, any linear machine can be driven as amotor, or alternatively as a generator depending on the drive type andirregularity sensed.

The correcting member of the present invention uses the flywheel seatedon a shaft of the drive unit as the rotor. An electromagnetic couplingbetween the rotor (constructed as a flywheel) and the stator of thelinear machine transfers a compensating torque to the rotating shaft tocompensate for rotation irregularities. The strength of the magneticcoupling and the corresponding thrust or retarding moment exerted on theshaft is controlled by altering the magnetic flux through the gap. Thisis achieved by changing the current supplied to the exciter coils of theelectrical machine, and/or by altering the gap, inclusive of a mediumpresent therein.

The present invention operates as a motor and as a generator dependingon the application of vibration forces. In the preferred embodiment, theinvention includes a switching arrangement which switches over thecorrecting member depending on the type of irregularities sensed. Inthis way, the linear machine is driven as an (accelerating) electricmotor when turning-rate decreases are sensed. Alternatively, the linearmachine is driven as a (braking) generator when turning-rate increasesare sensed. The energy recovered during generator operation can bestored in the manner of conventional energy recovery with use of thesame as a light machine.

In a preferred implementation of the invention used in conjunction withthe crankshaft of a motor vehicle internal combustion engine, theinvention includes a control arrangement that drives the correctingmember, i.e., the linear machine, as an engine or drive unit starter.

Many internal-combustion engine drive units cannot start from their ownstrength. They must first be started by an external source such as theconventional starter and be ramped up to the motor turning rate requiredfor self-operation.

It is only after this that they can continue to run from their ownforce. This requires, according to motor type, stroke volume, bearingfriction, etc., a rather large starting torque to be provided by thestarter. This is conventionally implemented with a gear on a massiveinertia mass or a flywheel seated on the drive unit shaft--in the caseof motor vehicles the crankshaft.

Conventional starters employ a battery-fed direct-current motor whichtransfers the necessary torque via a drive pinion to the flywheel. Onecommon starter motor is a so-called direct-current series closure motor,i.e., an electrical direct-current motor wherein the exciter or statorwinding is switched in series with the armature winding. In order tostart the engine, the drive pinion of the series-connection motor isbrought into engagement with a gear rim seated on the periphery of theflywheel disk under action of a magnetic switch-controlled engaginglever. After starting, this connection is again interrupted. Afree-wheeling coupling adapted for overload protection is typicallyarranged between the armature of the series-connection motor and thedrive pinion. This arrangement prevents the armature from being drivenat an undesirably high turning rate during the starting of theinternal-combustion engine. In further known starters, a meshing gearmechanically connects the armature of the series closure motor and thegear rim of the flywheel. The meshing gear facilitates "meshing" of thepinion into the gear rim. Thus these known starters are a component thatis quite expensive and is frequently subject to repair. The flywheel isalso an expensive component since it includes a gear rim for theengagement of the starter pinion on its outer circumference and othermarks for the control of the ignition processes in the motor.

The aforementioned preferred further developments of the invention,particularly in their use for internal-combustion engines, yield severaladvantages. For example, the correcting member operable as a starteraccording to the invention is a compact and simple construction. It is,in a sense, constructed "around the flywheel." The weight and thedimensions in the motor zone of the motor vehicle are therebydramatically reduced. The conventional starter for the motor vehicle,with its rotor, transmission gear and drive pinion become superfluous.Furthermore, the gear rim on the flywheel is eliminated, such that theflywheel is of a correspondingly simple construction with reducedproduction expenditure. Further, a mechanical "operative" transmissionof the thrust or retarding moment onto the flywheel is avoided and it isreplaced by a magnetic coupling linking the flywheel and stator. Thethrust or damping process of the invention therefore eliminatescontacting parts since the thrust or damping moment is developed fromelectromagnetic field forces. Furthermore, aside from the flywheel, nomovable parts are utilized. The correcting member starter configurationis subject to reduced wear. Further, the conventional light machine issuperfluous. As a result, therefore, the invention contemplates a singlecomponent to provide active vibration damping, starting or setting thedrive unit into operation and a current supply. This involves a clearreduction in costs.

In order to achieve appropriate active vibration damping, the correctingmember in the electrical machine, whether direct-current,alternating-current or three-phase-current machine, must transfer asufficiently great thrust or retarding moment onto the flywheel of thedrive unit in order to regulate shaft turning rate. In order to providea starter operation for internal-combustion engines, there areespecially well suited machine types that develop a strong torque andachieve a sufficiently high turning rate. The invention provides alinear machine, i.e., a rotating electric machine of a linear motor orlinear drive structure.

The linear motor preferably is implemented as an induction motor with ashort-circuit rotor, i.e., an asynchronous motor. Instead of a rotaryfield known, say, from such asynchronous motors, the exciter windings ofthe linear motor form a pure field of travel. The travelling magneticfield generated by the stator (or rotor) traverses the rotor (or stator)and induces therein annular or eddy-current flows. The correspondingmagnetic fields are entrained with the travelling field and, as aresult, exert the desired thrust force.

The flywheel seated on the rotating shaft preferably is adapted as therotor of such a linear motor. The transfer of the thrust or retardingmoment to the flywheel to influence the shaft turning rate occurs via anelectromagnetic coupling between the flywheel and the stator of thelinear motor. A high coupling efficiency is achieved when the gapbetween flywheel and stator of the linear motor is rather small,preferably on the order of 0.1 to 1.5 mm.

There are several advantages of linear motors. They are relativelysimple and sturdy construction, require minimal maintenance, are easy toregulate, and they provide great thrust forces (up to 1000 N). Further,upon over-increase of momentary turning rate, the linear motor functionsas a generator by returning energy into the network in the same mannerthat reversal of the direction of the travelling field retards movementof the rotating shaft.

In a rather simple implementation, the exciter coils generating thetravelling field are disposed on the stator proximate to only one sideof the flywheel, preferably only within a certain segment-type angularrange of the flywheel. However, with rising demands on the requiredstarting torque, the stator coils can be arranged to the full 360°scope. There the coils can be distributed uniformly or non-uniformly onthe one side of the flywheel. Alternatively, the coils can be arrangedon both sides of the flywheel for increased starting torque. The statorcoils, therefore, may be distributed within selected angular ranges orover the entire circumference on one or both sides of the flywheel. Thelinear motor of the invention is simply adapted for providing differentoutput ranges.

The flywheel is preferably fabricated of a metal such as iron. In orderfurther to increase conductively, the flywheel is coated or covered witha material of high conductivity, i.e., copper, and is disposed on theexterior surfaces disposed parallel to the stator coils. The eddycurrents induced in the conductive layer develop a secondary magneticfield which, as with the primary magnetic field, is perpendicular to thegap plane to ensure an optimal degree of coupling. Alternatively,short-circuited rotor windings may be arranged on the flywheel in suchmanner that the primary field and the secondary field are optimallyinterlinked.

This arrangement achieves a substantial increase in the resulting thrustor retardation force. The eddy currents induced in the flywheel aredisbursed undisturbed within the highly conductive layer or in the rotorwindings, so that the induced magnetic field is correspondingly greaterto provide a reinforced interaction with the exciter field.

Conventional linear motors provide a resulting thrust or retardationforces approximately proportional to the electrical conductivity of thematerial of the current-conducting rotor layers. Further, heat losses,namely, so-called eddy-current losses, in the flywheel are reduced to aminimum.

In respect to production, it is especially favorable to construct theflywheel as a circular steel disk and to coat the external surfacesfacing the air gap with a copper plate.

In order to achieve further increase in the thrust or retardation forceof the correcting member, in a further preferred embodiment, rotor coilsacted on with current are arranged in or on the flywheel in such mannerthat their magnetic field stands perpendicular to the gap plane.

Especially in the case of great deviations from desired turning rates itis expedient to construct the flywheel in such manner that it has aT-shaped cross section.

In this case, stationary exciter coils, for example, which generate theprimary field can be arranged both laterally and also radially on theflywheel exterior. In this manner, the exciter coils "embrace" theT-shaped end zone of the flywheel--similarly as in the case of ahigh-speed magnetic suspended railway. In this manner there is achieveda strong magnetic coupling between exciter coils and flywheel withsimultaneously compact and sturdy construction.

Alternatively the exciter coils can also be arranged in or on theflywheel and a material of high conductivity or short-circuited windingscan be arranged on the stator of the linear motor. In this manner thefunctions of moved and stationary base element are simply exchanged inrespect to the generation of primary or exciter field and secondaryinduced field with respect to the previously described arrangement. Theexciter coils on the flywheel generate the travelling field, whichinduces eddy currents in the stator, in order in interaction with thetravelling field to exert a thrust or retarding force on the flywheel.

This arrangement has the advantage that it can be adapted flexibly tothe dimensions in the motor zone of a motor vehicle. In consequence ofthe traveling movement of the moving field, only the stator or the rotorcoil arrangement has to span the path to be covered. The followingexecutions are possible. The stator can extend concentrically about theentire circumference on one or both sides of the flywheel. It forms aring or double ring. Simultaneously rotor coils are disposed in or onthe flywheel exclusively in a segment-type section of the flywheel.Alternatively, the stator can extent only over a certain anglearrangement and the allocated rotor coils can span the fullcircumference of 360°.

In especially layered exceptional cases it can be appropriate toconstruct the flywheel itself as a passive vibration eradicator or toarrange such an eradicator parallel thereto, in order to achieve anoptimal noise reduction by a combined active and passive vibrationdamping. In a preferred variant the flywheel is constructed from aninner rotating ring and an outer rotating ring arranged concentricallythereto, the rotating rings being elastically joined with one another,especially over a rubber layer.

Especially space-saving is a further flywheel variant of the correctingmember according to the invention. There the flywheel is inclined withrespect to its axis of rotation and has an outer rotating ring arrangedelastically hereto; it is expedient that the outer rotating ring isarranged with inclination with respect to the inner rotating ring. Ifthe flywheel has an inner rotating ring and an outer rotating ringarranged elastically thereto, it is expedient that the outer rotatingring is inclined to the inner rotating ring.

Finally, the invention proposes an especially simple turning-rateregulation for the active vibration system of the invention, which has ameasurement value receiver for the determination of rotationirregularities of the shaft, a correcting value giver engaged on outletside (in regulating technology called "regulator") for the generation ofcorrection values and correcting member, for example in the form engagedon outlet side of the correction value giver, which acts on the rotationof the shaft. Deviations from the momentary desired turning rate or thedesired angular segment velocity are continuously determined, from thesethere are derived correction values for the control of the correctingmember and finally, by the correcting member there is exerted anaccelerating or retarding force on the shaft-end namely in such mannerthat the desired momentary turning rate is continuously restored andmaintained.

In this manner the action of the correcting member leads to anadjustment of the rotation of the shaft, i.e., to a compensation of theinterfering vibrations caused by rotation irregularities and therewithto a damping of rotary vibration.

In one preferred embodiment, the measurement-value receiver has aturning-rate sensor mounted directly on the shaft, in particular aninductive or optical sensor, for the measurement of the momentaryturning-rate values or of the angular segment velocity of the shaft anda comparator for the formation of the regulating difference. Hereby therotation irregularities of the shaft to be corrected can be simplydetermined. The turning-rate sensor is allocated to individual anglesegments, for example a disk seated on the shaft or a gear wheel, andmeasures continuously the momentary values of the turning rate of theindividual angle segments. These measurement values are fed to thecomparator, which compares them with corresponding desired values. Theresult of this comparison is the regulating difference, i.e., a measurefor the rotation irregularities of the shaft. As respective desiredvalue a measurement value preceding in the sequence of the continuouslymeasured actual values, preferably the measurement value immediatelypreceding, or the mean value of several of these predecessor measurementvalues. The correcting member there responds preferably only when theregulating difference exceeds a given threshold value.

Advantageously the momentary values of the turning rate, however, canalso be fed to a differentiating member for the recovery of thedifferential turning rate or of the momentary angle-segmentacceleration, which is compared in the comparator with correspondingdesired values to determine the regulating difference. Here, too, in theselection of the desired values and the response of the correctingmember it is possible to proceed analogously to the precedingdesired-value selection and/or analogously to the preceding responsebehavior of the correcting member.

In another preferred embodiment, the measurement value receiver includesa vibration sensor for the measurement of every type of vibrations whichare due to rotation irregularities of the rotating shaft. The vibrationsensor is, for example, mounted in a motor vehicle, in any suitableplace, say on the body-work or in the interior of a vehicle, preferablyin the zone of the vehicle seats, i.e., where the noise levelaccompanying the interfering vibrations is especially representative ofinterfering vibrations or is found especially troublesome by the vehicleoccupants.

The vibration sensor is preferably a microphone, for example a movingcoil microphone, which is preferably arranged in the region of the heatsupports of the seats in a motor vehicle, and generates an inducedvoltage--proportional to the frequency of the troublesome sound waves.Further there come into consideration as vibration sensorsvibration-receivers which, for example, are mounted directly on thevehicle body-work, such as inductive receivers, capacitive receivers,piezo-receivers, resistance receivers (stretch-measuring strips), etc.

The measurement value receiver has a processing device coupled with theoutlet of the vibration sensor, which is designed for the derivation ofthe turning-rate momentary values or of the angular segment velocity ofthe shaft from the measured interference-vibration measurement values. Acomparator for the formation of the regulating difference receives thisinformation and operates as described above.

The interfering vibrations detected by the vibration sensor are then fedas measuring signal to the processing device. The latter evaluates ingeneral the amplitudes, frequencies and phases of the received measuringsignals and derives from them parameters of the shaft movement,especially the momentary values for the shaft turning rate or theangular segment velocity or the angular segment acceleration. For thisderivation it is necessary to know a transfer function which takes intoaccount the influences of the transmission medium, for example, gears,vehicle body-work, air, etc. on the propagation of the interferingvibrations (from the interfering vibration source--namely the shaftdriven by the drive unit or located therein--to the measuring site). Thetransfer function is preferably determined experimentally.

From the interfering vibration measurement values measured with the aidof the vibration sensor at an arbitrary place on the measuring site,then, with the aid of the transfer function for this measuring sitethere are determined the actual parameters of the shaft movement of therespective rotating shafts. The derived momentary measurement magnitudesare then fed to the comparator, which performs a comparison with thedesired values in order to establish, from them, the regulatingdifference.

The comparator--both in the first alternative measurement valuereceiver, as well as in the second alternative measurement-valuereceiver--preferably is a computer which processes various regulatingstrategies. These may include a characteristic curve field, wherewithall the rotation irregularities occurring--and therewith interferencevibration frequencies of the shaft--can be effectively damped.

The correction value giver, engaged on outlet side of the comparator,derives from the regulating difference the correction values for thecompensation of the rotation irregularities--and namely in such mannerthat there is achieved a favorable time course of the regulatingprocess. Preferably the correction value giver is equipped with a devicefor the signal amplification, so that advantageously the arrivingregulating difference signal is forwarded amplified to the correctingmember.

The appropriate regulating strategy may depend on the operating type ofthe drive unit. For example, in a fixed-value regulation a given value,constant in time, of the momentary turning rate is maintained within acertain turning rate range. In a sequence regulation, in contrast, agiven value, variable over time, of the turning rate is brought about.

Further, the correcting member is preferably operated in such mannerthat upon sensing of a regulating difference, it exerts a force on ashaft either impulsively, or uniformly over a relatively long period oftime. If the same rotation irregularities should repeat periodically,then it is worth recommending that the correction of the turning rate becontrolled in counterphase thereto. In the case of other irregulardeviations from the desired turning rate over a relatively long periodof time the correcting member acts on the turning rate of the shaftcorrespondingly uniformly damping or accelerating.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram representation of an active vibrationdamping system according to the invention;

FIG. 2 is a side view of a flywheel and correcting member of thevibration damping system according to the invention in FIG. 1;

FIG. 3 is a vertical section along the line III--III in FIG. 2; and

FIG. 4 is a section view analogous to FIG. 3 of a flywheel variantaccording to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following detailed description explains the invention in the contextof providing active vibration damping for a rotating crankshaft 12 of amotor vehicle internal combustion engine for the sake of simplicity. Itshould be understood, however, that the invention is not intended to berestricted to this particular implementation, but can be utilized in anydrive unit which includes a rotating shaft or the like.

FIG. 1 shows an active vibration damping system for compensatingcrankcase interfering vibrations and noises proceeding therewith. Theseare due primarily to rotary irregularities of the crankshaft 12 operatedby the combustion engine.

According to FIG. 1 a turning-rate sensor 2 is mounted in a suitableplace on the crankshaft 12. The turning rate sensor 2 detects severalangular segments of the crankshaft 12 and continuously monitors themomentary crankshaft turning or angular rate or angular segmentvelocity. The sensor 2 may be implemented as a rotation governor or asan inductive turning-rate sensor, which is allocated to individual anglesegments of a flywheel or of a gear wheel on the crankshaft 12. Anoptical turning-rate sensor which measures the momentary shaft turningrate on the basis of an interruption of a light source due to therotation of the shaft is also envisioned. The shaft turning-ratedetection can be obtained in a manner analogous to the wheelturning-rate and slip measurement known from ABS systems.

The turning-rate sensor 2 detects momentary turning rates of the shaftand supplies signals corresponding thereto to a comparator 4. Thecomparator 4 is preferably implemented as a digital computer, whichcompares a digitized value corresponding to the momentary turning ratewith predetermined desired values. As a result of such comparison, thecomparator 4 generates a regulating difference signal corresponding tomomentary or periodic rotary irregularity of crankshaft 12. This signalis supplied to an output circuit 6 to generate appropriate correctionsignals. The output circuit 6 provides the correction signals to acorrecting member 8 implemented as a linear electrical machine. Thecorrecting member 8 provides a compensating torque to the crankshaft 12such that the predetermined momentary angular or turning-rate of thecrankshaft is restored.

In this manner disturbances of the crankshaft turning rate areeradicated already in their arising, so that interference vibrations andtherewith associated noises in the motor vehicle cannot arise at all.

FIGS. 2 and 3 illustrate one embodiment of the correcting member 8according to the invention in greater detail. As noted, the correctingmember 8 is implemented as a linear motor of the vibration-dampingsystem. The correcting member 8 comprises a disk-shaped flywheel 10seated on the crankshaft 12 of the internal combustion engine. Theflywheel 10 is adapted for use as a movable base element or rotor of alinear motor 14 that receives a thrust or retarding moment.

The flywheel 10 includes an outer rotating ring 16 and an inner rotatingring 18 concentric to the outer ring 1 about an axis of rotation. Anannular rubber layer 20 elastically joins the outer and inner rotatingrings 16 and 18. The inner rotating ring 18 is fitted to a hub 22 whichis seated firmly on the crankshaft 12. In this manner, the flywheel 10provides a rotary vibration eradicator which counteracts passive rotaryirregularities of the crankshaft 12.

A pair of three-coil stator coils 24 flank the opposed sides of theouter rotating ring 16. In the preferred embodiment, the stator coils 24are uniformly positioned within a segment-type angular section of theflywheel 10. The stator coils 24 are slightly spaced from the outerrotating ring 16 to define an air gap 26. The gap 26 is preferably quitenarrow, on the order of between 0.1 and 1.5 mm.

The stator coils 24 are supported by a stationary holding yoke 28overlapping the flywheel 10 in the manner of a yoke. Preferably, theholding yoke 28 is coupled with on the crankshaft 12 (not shown) androtatable therewith so that the stator coils 24 and the flywheel aresubjected to common vibration. In this way, the reciprocal alignmentbetween the flywheel and stator coils and the gap 26 are substantiallyconstant.

The stator coils 24 receive current in a known manner from a currentsupply (not shown) based on the correction signal generated by theoutput circuit 6 and generate a travelling magnetic field whichtraverses an annularly closed electric field developed in the outerrotating ring 16, and thus induces an annular voltage. As a result,voltage there flows in annular or eddy-current flows in the outerrotating ring 16 having corresponding magnetic fields which are linkedwith the travelling field of the stator coils 24 to exert a force intangential direction on the flywheel 10. Depending on the type of therotary irregularities, the turning direction of the travelling field ischosen relative to the turning direction of the crankshaft such thatwhen unacceptably low momentary turning rates are sensed, a thrust forceis applied to the flywheel. When unacceptably high momentary turningrates are sensed, a retarding force is applied until an evening up ofthe crankshaft rotation or a rotary vibration damping is achieved. Themagnitude of thrust or retarding force can be controlled simply byaltering the current flowing through the stator coils 24 and therebyadjust of the magnetic flux density through the gap 26.

The outer rotating ring 16 of the flywheel 10 is made of steel andcovered with copper plating on its two side surfaces facing the statorcoils 24. Hereby high eddy currents can be induced in the side surfacesand correspondingly high thrust or retardation forces. A furtherheightening of the thrust force can be achieved by the rotor coils 29arranged on the flywheel 10 and acted upon with a current (as indicatedin FIG. 1 by broken lines). There the rotor coils 29 are arranged insuch a way that their magnetic field stands perpendicular to the gapplane and they are acted upon in such manner that the fields of therotor coils 29 and stator coils 24 are maximally strengthened. The fieldof the rotor coils 29 there can be a unidirectional field or atravelling field adapted to the phases of the field of the stator coils24. In the last-mentioned case the thrust or retardation force acting onthe crankshaft is based above all on the "entrainment" of the field ofthe rotor coils 29 by the travelling field of the stator coils 24.

As already stated, in the present example of execution the flywheel 10is additionally constructed as a passive rotary vibration eradicator,the annular rubber layer 20 of which elastically connects the innerrotating ring 18 with the outer rotating ring 16, eradicating possiblerotary vibrations. When the elastic connection of the two rotating rings16, 18--as in the embodiment represented--has electrically insulatingproperties, then in addition to the vibration damping there is alsoyielded still an electrical advantage: the annular currents induced inthe outer rotating ring 16 cannot pass over into the inner rotating ring18, and are concentrated, therefore, on the torque-favorable peripheralzone of the flywheel 10.

In FIG. 4, there is represented a variant of the flywheel 10. Here, theouter rotating ring 16 of the flywheel 10 is inclined with respect tothe flywheel plane by an angle 30. The other components of the starteraccording to FIGS. 2 and 3 are arranged in correspondence to thisorientation. In this manner the correcting member 14 can be adaptedespecially simply to the spatial relations in the zone of the flywheel10 in its construction, without impairing its efficiency.

According to FIG. 3 there is allocated to the correcting member 8 aschematically represented electronic circuit 32 which can drive it in amotor vehicle, besides for turning-rate regulation, for two furthertypes of operation: In actuating the starter key, the correcting member8--where the linear motor 14--functions as a motor for the starting ofthe internal-combustion engine; it can then be switched over into agenerator operation. In the last-mentioned generator operation the rotorcoils 29 are acted upon over slip contacts (not shown here) with acurrent generating a magnetic field. By reason of the flywheel movement,this field travels relatively to the gap plane and induces or generatesin the stator coils 24 a voltage which supplies the vehicle withelectric energy in travelling operation. In this manner the linear motor14 in a motor vehicle can take over also the function of a starter forthe starting of the internal-combustion engine and of a light machinefor the energy supplying of the vehicle. The circuit 32 is designedexpediently as a priority circuit, which switches the linear motor 14over into the generator operation whenever no turning-rate regulation isrequired, for example in low turning-rate ranges. obviously, the linearmotor 14 can be used for turning-rate regulation and for currentgeneration simultaneously--with lower current yield--because the voltageinduced in the stator coils 24 again evokes eddy currents the magneticfields of which exert a retarding force on the flywheel 10. Accordingly,an active vibration damping system meeting the aforestated objectiveshas been described. The system detects whether the angular rate of ashaft is different from a known value and provides a compensating torquein response. When implemented as a linear machine into an internalcombustion engine for motor vehicles, the system greatly reduces thenoises generated. In addition, electrical current may be induced andutilized as necessary.

We claim:
 1. A method for active vibration damping a drive unit with atleast one rotating shaft, a flywheel seated on the shaft adapted for useas a movable base element of a linear electric motor, a stationary baseelement of the linear electric motor, and a gap separating the movablebase element from the stationary base element, the methodincluding:sensing rotational irregularities of the shaft and providing asensing signal; comparing the sensing signal with selected values andderiving a correction signal; and applying the correction signal to thelinear electric motor to increase the rotation of the shaft in a firstmode wherein current is supplied to the stationary base element and todecrease the rotation of the shaft in a second mode wherein current isdrawn from the stationary base element.
 2. The invention as in claim 1wherein the sensing step includes measuring the momentary angular rateor the angular segment velocity directly from the shaft.
 3. Theinvention as in claim 1 wherein the sensing step includes measuringresulting interference vibrations and deriving a momentary angular ratevalue or an angular segment velocity value of the shaft.
 4. Theinvention as in claim 1 wherein the correction signal is appliedperiodically over a relatively long period of time.
 5. A drive unithaving an active vibration damping system comprising:at least onerotating shaft; a flywheel seated on the shaft adapted as a movable baseelement of a linear electric motor which is operable in a first mode todraw current and operable in a second mode to supply current; astationary base element separated from the flywheel by a gap; and acontrol circuit disposed for sensing rotational irregularities of theshaft and providing control signals to the linear electric motor forgenerating a compensating magnetic flux in the linear electric motor. 6.The invention as in claim 5 wherein the control circuit comprises:ameasurement sensor disposed for determining rotation irregularities onthe shaft and providing sensing signals; a procesor disposed forcomparing the sensing signal with selected correction values and forgenerating the control signals.
 7. The invention as in claim 6 whereinthe measurement sensor includes an angular segment turning-rate sensormounted on the shaft.
 8. The invention as in claim 6 wherein themeasurement sensor comprises a vibration sensor disposed to detectinterference vibrations resulting from turn-rate irregularities of therotating shaft.
 9. The invention as in claim 5 wherein the stationarybase element and the flywheel are arranged such that the gap separatingthe stationary base element and the flywheel can be selectively varied.10. The invention as in claim 9 further comprising switching meanscoupled with the linear electric motor and with the control circuit foroperating the linear electric motor in the first mode upon the receiptof a first signal from the control circuit and for operating the linearelectric motor in the second mode upon the receipt of a second signalfrom the control circuit.
 11. The invention as in claim 10 wherein theshaft is a crankshaft of a motor-vehicle internal-combustion engine, andwherein the control circuit provides third signals to drive the linearelectric motor as a starter during a starting operation of the driveunit.
 12. The invention as in claim 11 further including a plurality ofexciter coils disposed on the stationary base element.
 13. The inventionas in claim 11 wherein the stationary base element includes spacedexciter coils disposed proximate to at least one side of the flywheel.14. The invention as in claim 13 wherein the gap separating thestationary base element and the flywheel is arranged in a gap plane andthe flywheel includes a layer of material of high conductivity adaptedto present an induced magnetic field in the layer perpendicular to thegap plane.
 15. The invention as in claim 13 wherein the gap separatingthe stationary base element and the flywheel is arranged in a gap planeand further comprising a plurality of rotor coils arranged on theflywheel presenting an induced magnetic field perpendicular to the gapplane.
 16. The invention as in claim 13 wherein the the flywheel has aT-shaped cross section.
 17. The invention as in claim 13 wherein theflywheel is constructed as a passive rotary vibration eradicator. 18.The invention as in claim 17 wherein the flywheel comprises an innerrotating ring, an outer rotating ring arranged concentrically thereto,and a rubber layer elastically joining the outer and inner rotatingrings.
 19. The invention as in claim 18 wherein the flywheel is inclinedwith respect to its axis of rotation.
 20. The invention as in claim 19wherein the outer rotating ring is inclined with respect to the innerrotating ring.